FIG. 25 shows a first exemplary configuration of a conventional multicarrier transmission system (Patent Document 1).
In FIG. 25, a transmitter of the conventional multicarrier transmission circuit includes modulation circuits 1001 to 100N for each user, a Tx filter bank 101 and a transmitting circuit 102. A receiver includes a receiving circuit 103, an Rx filter bank 104 and demodulation circuits 1051 to 105N for each user.
The modulation circuits 1001 to 100N in the transmitter modulate (map) data 1 to N for each user, respectively. The Tx filter bank 101 converts respective modulated signals to respective predetermined carrier frequencies, which are in turn combined and transmitted by the transmitting circuit 102. The Rx filter bank 104 in the receiver filters multicarrier signals received at the receiving circuit 103 for each carrier frequency, and the demodulation circuits 1051 to 105N demodulate data 1 to N for each user, respectively.
FIG. 26 shows a second exemplary configuration of a conventional multicarrier transmission system. Here, an example is shown in which, in the conventional multicarrier transmission system shown in FIG. 25, a user A uses an unused frequency band to transmit a signal when other users 8, C and D have already occupied frequency bands for communication.
A serial-parallel converter 110 in the transmitter serial-to-parallel converts data for the user A, modulation circuits 1111 and 1112 modulate serial-parallel converted data, respectively. A Tx filter bank 112 converts each of modulated signals A1 and A2 for the user A to a predetermined carrier frequency, so as to be allocated to an unused frequency band and transmitted by a transmission circuit 113. Meanwhile, an Rx filter bank 115 in the receiver filters multicarrier signals received at a receiving circuit 114 for each carrier frequency for frequency conversion, and demodulation circuits 1161 to 1162 demodulate modulated signals A1 and A2 for the user A, respectively. The demodulated modulated signals A1 and A2 are parallel-serial converted by a parallel-serial converter 117 and restored to data for the user A.
FIG. 27 shows an exemplary configuration of a conventional orthogonal frequency division multiplexing (OFDM) transmission system.
In FIG. 27(a), a conventional OFDM transmission system includes an OFDM modulation circuit 120 on the transmission side, and an OFDM demodulation circuit 121 on the reception side. The OFDM modulation circuit 120 includes a serial-parallel converter 122, modulation circuits 1231 to 123N and an inverse fast Fourier transform (IFFT) circuit 124. The OFDM demodulation circuit 121 includes a fast Fourier transform (FFT) circuit 125, demodulation circuits 1261 to 126N and a parallel-serial converter 127.
Usually, with the orthogonal frequency division multiplexing-time division multiple access (OFDM-TDMA) scheme, which divides users' signals into time slots to distinguish the users according to time, the users' signals that are divided into time slots are serial-to-parallel converted by the serial-parallel converter 122, and each of the parallel-output signals is modulated by each of the modulation circuits 1231 to 123N, independently. Subsequently, the parallel-output modulated signals are converted to time domain by the IFFT circuit 124, and transmitted as multicarrier signals.
Meanwhile, in the OFDM demodulation circuit 121, after establishing OFDM frame synchronization, the signals are converted to frequency domain by the FFT circuit 125, and demodulated by the demodulation circuits 1261 to 126N for each sub carrier. The demodulated signals are input into the parallel-serial converter 127, and restored from per-sub carrier signals to the original one-system signals.